Al Jazeera's Rob Reynolds in Philadelphia said Clinton had struck a defiant tone and made clear that she was going to continue the battle for the nomination.

But Clinton had been hoping for a big win to keep alive her chances of becoming the Democratic nominee to face Republican John McCain in November's election, and it was unclear if the eight-point victory was enough to bolster her campaign.

Clinton had seen her opinion poll lead in the state slip from more than 20 per cent to a single digit after a series of wins by Obama in other states.

Protracted battle

Pennsylvania's final delegate count is not expected until later Wednesday as many counties are split into multiple congressional districts.

However, an analysis of returns by NBC indicated

Clinton had won at least 75 delegates and Obama at least 65, with about 99 per cent of districts reporting.

After the 15-month race, neither Democrat is expected to reach the tally of 2,025 nominating delegates to claim the nomination outright.

Reynolds said that "what Clinton wants to do is try to make her case to the superdelegates - the special delegates who are mostly party officials who are not beholden at this point to either candidate. They can choose who they support."

"Clinton is going to go to them now and say, 'Look, I'm winning in the big states - Pennsylvania, Ohio, California, New York. I'm winning in all these big popular states where Democrats have to win in the fall against the Republicans [in the US presidential election]'."

However, Reynolds said that Clinton's campaign had less money than Obama, casting doubt over whether she can continue a protracted battle against her rival.